function out=whitenCol(in)
% out=whitenCol(in); 
% Whitens colums of the matrix in (each column has zero mean and unit
% variance).
% Example: 
%           var(whitenCol(rand(20,3)),[],1)
%           mean(whitenCol(rand(20,3)),1)
out=bsxfun(@rdivide,bsxfun(@minus, in, mean(in,1)), std(in,[],1)); 
